According to the state of the art, automatic transmissions, particularly for motor vehicles, comprise planetary gearsets, which are shifted using friction and/or shifting elements, such as clutches and brakes, and which are typically connected to a start element that is exposed to a slip effect and optionally provided with a lock-up clutch, for example, a hydrodynamic torque converter or a fluid clutch.
Within the scope of the Applicant's DE 101 15 983 A1, a multi-speed transmission is described, for example, with a drive shaft that is connected to a front-mounted gearset, an output shaft that is connected to a rear-mounted gearset, and a maximum of seven shifting elements, via whose selective engagement at least seven forward gears can be shifted without range shifts. The front-mounted gearset is formed by a shiftable or non-shiftable planetary gearset or a maximum of two non-shiftable front-mounted planetary gearsets connected to one another. The rear-mounted gearset is configured as a two-carrier/four-shaft transmission with two shiftable planetary gearsets and having four free shafts. The first free shaft of this two-carrier/four-shaft transmission is connected to the first shifting element, the second free shaft to the second and third shifting elements, the third free shaft to the fourth and fifth shifting elements and the fourth free shaft is connected to the output shaft. According to the invention, a multi-speed transmission with a total of six shifting elements is proposed, which additionally connects the third free shaft or the first free shaft of the rear-mounted gearset with a sixth shifting element. For a multi-speed transmission with a total of seven shifting elements, it is proposed according to the invention that the third free shaft be additionally connected to a sixth shifting element and the first free shaft additionally to a seventh shifting element.
Several further multi-speed transmissions are also known, by way of example, from the Applicant's DE 101 15 995 A1, where four shiftable planetary gearsets coupled to one another and six or seven shifting elements engaged to one another are provided, via whose selective closure a rotational speed of a drive shaft of the gearbox can be transmitted to an output shaft of the gearbox in a way that nine or eleven forward gears and at least one reverse gear can be shifted. Depending on the gear diagram, two or three shifting elements are closed in each gear, where, by changing from one gear to the, in each case, next higher or lower gear, only one engaged shifting element is disengaged at a time and a previously disengaged shifting element is engaged, to avoid range shifts.
Furthermore, in an undisclosed patent application in conformity with its kind, DE 10 2005 002 337.1 by the Applicant, a multi-speed transmission with one drive shaft, one output shaft, four individual planetary gearsets coupled to one another and five shifting elements is proposed, where eight forward gears can be shifted into without any range shifts, i.e., in a way that by changing from a forward gear to the next higher or lower forward gear only one of the previously engaged shifting elements is disengaged and only one of the previously disengaged shifting elements is engaged at a time. The multi-speed transmission also shows a reverse gear. In all forward gears and the reverse gear, three shifting elements are engaged at a time. With respect to the kinematic coupling of the four planetary gearsets with one another and with the drive shaft and output shaft, it is provided that one carrier of the fourth planetary gearset and the drive shaft are connected to one another and form the first shaft of the gearbox, one carrier of the third planetary gearset and the output shaft are connected to one another and form a second shaft of the gearbox, one sun gear of the first planetary gearset and one sun gear of the fourth planetary gearset are connected to one another and form a third shaft of the gearbox, one ring gear of the first planetary gearset forms a fourth shaft of the gearbox, one ring gear of the second planetary gearset and one sun gear of the third planetary gearset are connected to one another and form a fifth shaft of the gearbox, one carrier of the first planetary gearset and one ring gear of the third planetary gearset are connected to one another and form a sixth shaft of the gearbox, one sun gear of the second planetary gearset and one ring gear of the fourth planetary gearset are connected to one another and form a seventh shaft of the gearbox and one carrier of the second planetary gearset forms an eighth shaft of the gearbox. With respect to the kinematic coupling of the five shifting elements with the four planetary gearsets and drive shaft and output shaft, it is provided that the first shifting element is arranged in the power flow between the third shaft and a gearbox housing, the second shifting element in the power flow between the fourth shaft and the gearbox housing, the third shifting element in the power flow between the first and fifth shaft, the fourth shifting element either between the eighth and second shaft or between the eighth and sixth shaft, as well as the fifth shifting element either between the seventh and fifth shaft, or between the seventh and eighth, or between the fifth and eighth shaft.
Automatic shiftable vehicle transmissions in planetary design have in general been described from the state of the art on many occasions, and are subject to continuous development and improvements. These transmissions should feature a sufficient number of forward gears as well as one reverse gear and excellently suitable gear ratios for motor vehicles, with a high overall spread as well as favorable steps. Furthermore, they should allow a high start gear ratio in the forward direction and include a direct gear, and additionally be suited for use in both in passenger cars and commercial vehicles. In addition, these transmissions should require low manufacturing expenditure, in particular a small number of shifting elements, and avoid double shifts during sequential gear shifts, so that only one element at a time is shifted with shifts in a defined gear group.
The object of the present invention is to propose a multi-speed transmission of the type mentioned above with at least eight shiftable forward gears free of range shifts and at least one reverse gear, where by using a total of four planetary gearsets, a preferably small number of shifting elements are required. In addition, the gearbox should feature a large ratio spread at comparably harmonic gear shifting, showing a favorable degree of efficiency, i.e., comparatively low drag and gearing losses—in the main driving gears at least.